Series Resistor Calculator
Calculate total resistance for up to three resistors in series.
Interactive Electrical Calculator
Series Resistor Calculator
Calculate total resistance for up to three resistors in series.
Result
Enter values and calculate.
About the Series Resistor Calculator
Use the Series Resistor Calculator below to work through component-level calculations for resistors, capacitors and basic AC circuit behavior in seconds, right in your browser. Calculate total resistance for up to three resistors in series. Reactance, resonance and time-constant calculations explain why a circuit behaves differently at different frequencies, which pure DC thinking does not capture.
Electronics hobbyists, students and engineers designing or troubleshooting small circuits typically reach for a tool like this to double-check a number before it goes into a real installation.
How the calculation works
The calculator is built around this relationship:
Req = R1 + R2 + R3.
Where each input maps to a field in the calculator above:
- R1 in Ω.
- R2 in Ω.
- R3 in Ω.
You can adjust any of these values as many times as you like; the result updates on every change with nothing sent off your device.
A worked example
For example, start with 100 Ω for r1, 220 Ω for r2 and 330 Ω for r3. Press Calculate and the Series Resistor Calculator returns the result instantly — then change one field at a time to see how sensitive the answer is to that particular input.
When to use the Series Resistor Calculator
Typical reasons people reach for the Series Resistor Calculator:
- Picking a resistor or capacitor value for a specific circuit target.
- Checking a component combination before ordering parts or building a prototype.
- Working out a circuit's behavior at a specific frequency.
- Verifying a calculated value against a datasheet or standard component range.
Good practice: Reactance is frequency-dependent, so a capacitor or inductor calculation is only valid at the specific frequency it was calculated for.
Also worth knowing: Series and parallel combination rules are opposite for resistors and capacitors, which is a common source of mix-ups when switching between the two.
Frequently asked questions
What does the Series Resistor Calculator calculate?
Calculate total resistance for up to three resistors in series.
Is the result exact enough to build from?
The formula above is applied exactly to the values you enter, so the math itself is precise. Real-world results can still differ due to component tolerances, temperature, installation method, equipment efficiency and local code requirements, so treat the output as a strong planning estimate and verify final designs against manufacturer data and the electrical code that applies to your installation.
Do I need to sign up or install anything to use it?
No sign-up, download or installation is needed. The Series Resistor Calculator runs entirely in your browser and is free to use.
Why does this calculation matter in practice?
Reactance, resonance and time-constant calculations explain why a circuit behaves differently at different frequencies, which pure DC thinking does not capture.
Can I use this on a phone, or does it need a desktop?
The Series Resistor Calculator works on any modern browser, phone or desktop, and recalculates as soon as you press Calculate. If a result looks off, double-check that every field is filled in with the unit shown next to it (mixing up units, such as W with kW, is the most common cause of an unexpected answer) and re-enter the values.